FIELD OF THE INVENTION
The invention relates in general to the field of semiconductors, and specifically to a process for producing an integrated semiconductor memory configuration and to a semiconductor memory configuration produced using the process.
Semiconductor-based memory configurations usually comprise a number of memory cells which each have a selection transistor and a storage capacitor connected to the selection transistor. During a production process for such semiconductor memory configurations, it is usual to apply first electrodes over conductive connections, a respective one of the conductive connections connecting one of the first electrodes to a respective one of the selection transistors. A storage dielectric is applied over the first electrode and in turn has a second electrode applied to it, so that the first and the second electrode as well as the intermediate storage dielectric form a storage capacitor which is conductively connected to one of the selection transistors.
The use of new types of ferroelectric materials as the storage dielectric for storage capacitors allows semiconductor memories to be produced that do not lose their information (stored in the form of electric charge) after a supply voltage failure, and whose memory contents do not have to be refreshed at regular intervals as a result of leakage currents.
A critical factor for the use of most of the previously known ferroelectric materials of this type is their processing within a semiconductor process. Most ferroelectric materials of this type are deposited at high temperatures in an atmosphere containing oxygen. The use of such ferroelectric materials in the process described above, in which the storage dielectric is applied over the first electrode, which in turn is situated above a conductive connection to one of the selection transistors, results in oxidation of the conductive connection because, during deposition of the ferroelectric materials, oxygen diffuses through the first electrode in the direction of the conductive connection and oxidizes the latter. Oxidation of the conductive connection interrupts the electrical connection between the storage capacitor and the selection transistor of a memory cell, with the result being that the latter is no longer functional.
Solutions for preventing oxidation of the conductive connection during deposition of a ferroelectric storage dielectric call for applying barrier layers between the conductive connection and the first electrode, in which case the barrier layers have to be electrically conductive but capable of resisting oxidation and diffusion of oxygen. A disadvantage of the use of barrier layers is that it is hard to find suitable materials that are electrically conductive, impermeable to oxygen, capable of resisting oxidation and that can be suitably applied to the conductive connections.
A process for producing an integrated semiconductor memory configuration having a ferroelectric storage dielectric without using barrier layers is described in U.S. Pat. No. 5,439,840. In this described process, the first electrodes, the storage dielectric and the second electrode are applied over an insulation layer which is situated above selection transistors, using deposition processes. Subsequently, contact holes extending to the selection transistors are produced through the second electrode, the storage dielectric, the first electrode and the insulation layer and can be used to make electrical contact between the second electrode and the selection transistor. The particular disadvantage of this is the complex application of a further insulation layer in the contact hole in order to provide electrical insulation between the first electrode and the second electrode.